Supplemental funds are requested to continue research developments related to this grant but currently supported by developmental funds from a Cancer Center Core grant to the McArdle Laboratory. A cell-transplant approach will be used to identify new hepatocyte phenotypes with altered proliferation controls that arise during the premalignant phase of chemically-induced hepatocarcinogenesis in the adult rat. Preliminary data indicate that heterogeneous cell suspensions, isolated from rat livers (donors) containing neoplastic nodules, can be fractionated by centrifugal elutriation. Cell fractions will be assayed for progenitor cells of enzyme-altered, putative premalignant liver colonies by transplantation to syngeneic rats (hosts). A new cell-surface marker system will be developed that involves immunofluorescent localization of cell-surface histocompatibility antigens of F344 and Wistar-Furth (WF) inbred rat strains. The marker studies will require, as a working model, F344 (RT1 lvl/RT1 lvl haplotype) donor liver cells transplanted into livers of F1 hybrid rats (F344xWF) (RT1 lvl/RT1u haplotype). F344 anti-WF alloantiserum (anti-FTu haplotype) will be used to localize F344 liver colonies in vivo. Methods for non-destructive immunofluorescent identification of cells in vitro will be explored. Centrifugal elutriation will be applied to the in vitro stage of the in vivo (donor) yields in vitro yields in vivo (host) cell-transfer sequence to 1) produce subpopulations of donor liver cell suspensions enriched with progenitor cells for liver colonies, and 2) produce subpopulations expressing either the RT1 lvl/RT1 u haplotype or the RT1 lvl/RT1 lvl haplotype from hepatic cells of F1 (F344xWF) host rats containing liver colonies developed from F344 donor liver cells.